Mechanical properties of steel bars.

The utilization of rice husk ash (RHA) as a cement substitute in concrete can mitigate the environmental issues caused by concrete production. This study is the first investigated the effect of different concentrations of multiwall carbon nanotubes (MWCNTs) on the shear behaviour of RHA-reinforced concrete (RC) beams. Three RHA RC beams incorporating different MWCNTs concentrations (0%, 0.1%, and 0.2%) were subjected to shear failure tests, with shear behaviour evaluated based on load-deflection capacity, failure load, strain distribution, and crack development morphology. The results indicate that the incorporation of well-dispersed MWCNTs (0.1%) significantly enhances the shear resistance of RHA RC beams. Specifically, with the addition of 0.1% MWCNTs, the first crack load, initial stiffness, and ultimate shear capacity increased by 34.78%, 38.4%, and 4.76%, respectively, while midspan deflection and ductility improved by 23.19% compared to the control specimen. However, excessive MWCNTs incorporation negatively impacted shear capacity, as the inclusion of 0.2% MWCNTs led to an 8.57% reduction in the ultimate shear capacity of the RHA RC beam. Additionally, the experimental results were compared with predictions from several models, including the ACI 318 model, Eurocode 2–05 model, Canadian standard, Bazant and Kim, Zsutty, and Collins and Kuchma models. The comparison revealed that the Eurocode 2–05 model, Canadian standard, and Zsutty models provide reliable predictions of the shear behaviour of RHA RC beams, with an error margin within 20%. The findings suggested that well-dispersed MWCNTs can play a role in improving the initial stiffness and ductility of RHA RC beams, enhancing the shear resistance of the beams, delaying shear failure, and preventing brittle failure of the beams. Furthermore, the improvement of the performance of RHA sustainable concrete components by MWCNTs contributes to the sustainable development of the construction industry.

稻壳灰（rice husk ash, RHA）作为混凝土的水泥替代材料，可缓解混凝土生产带来的环境问题。本研究首次探究了不同掺量的多壁碳纳米管（multiwall carbon nanotubes, MWCNTs）对稻壳灰增强混凝土（RHA-reinforced concrete, RC）梁抗剪性能的影响。本次试验共制备3根掺有不同MWCNTs掺量（0%、0.1%、0.2%）的RHA-RC梁，开展抗剪破坏试验，并通过荷载-挠度性能、破坏荷载、应变分布及裂缝开展形态对其抗剪性能进行评估。研究结果表明，掺入分散性良好的0.1% MWCNTs可显著提升RHA-RC梁的抗剪承载力。具体而言，与基准试件相比，掺入0.1% MWCNTs后，初裂荷载、初始刚度及极限抗剪承载力分别提升34.78%、38.4%及4.76%，跨中挠度与延性则较基准试件提升23.19%。但过量掺入MWCNTs会对梁的抗剪性能产生负面影响：掺入0.2% MWCNTs会使RHA-RC梁的极限抗剪承载力降低8.57%。此外，本试验结果还与ACI 318模型、Eurocode 2–05模型、加拿大国家标准、Bazant与Kim模型、Zsutty模型以及Collins与Kuchma模型的预测结果进行了对比。对比结果显示，Eurocode 2–05模型、加拿大国家标准及Zsutty模型对RHA-RC梁抗剪性能的预测结果可靠，误差范围在20%以内。研究发现，分散性良好的MWCNTs可有效改善RHA-RC梁的初始刚度与延性，提升梁的抗剪承载力，延缓剪切破坏发生，避免梁发生脆性破坏。进一步而言，通过MWCNTs优化稻壳灰基可持续混凝土构件的性能，有助于推动建筑业的可持续发展。